The charges relate to samples taken earlier this year from 45 horses at the Newmarket, eastern England, yard owned by the leading Godolphin outfit.

Analysis of the samples revealed that 11 contained traces of the banned anabolic steroids ethylestranol and stanozolol.

Godolphin owner Sheikh Mohammed bin Rashid Al Maktoum reacted to what has been described as racing's biggest doping scandal in recent years by shutting the stables and ordering a full-scale internal investigation.

The sheikh, one of racing's leading figures and the ruler of Dubai, said he was "appalled and angered" by the revelations.

Al Zarooni has said the situation was a "catastrophic error" and claimed that he did not realise he was in breach of racing rules by administering the drugs.

The BHA said on Wednesday that he had told investigators that a further four horses that were not tested were also given the banned substances.